This research project supports studies on the control, the regulation and the function of cytosolic calcium. We are studying: 1) The site and mode of action of parathyroid hormone, of calcitonin, of the metabolites of vitamin D and of cyclic nucleotides on the cell calcium metabolism; 2) The interrelationship among calcium, phosphate and hydrogen ion in cellular function; 3) The role of parathyroid hormone, cyclic AMP and calcium on H ion secretion; and 4) The role of H ion on the cellular transport of phosphate and calcium. BIBLIOGRAPHIC REFERENCES: Borle, A. B., Methods for assessing hormone effects on calcium fluxes in vitro In: Methods In Enzymology. B. O'Malley and J. Hardman, eds. Academic Press, New York 39: 513-573, 1975. Borle, A. B., Regulation of cellular calcium metabolism and calcium transport by calcitonin. J. Membrane Biol. 21: 125-146, 1975.